1. Field of the Invention
The present invention relates to visual processing devices, display devices, and integrated circuits, and in particular relates to visual processing devices, display devices, and integrated circuits in which the contrast of an image is adjusted.
2. Description of the Related Art
Conventional color television receivers have performed contrast adjustment in order to adjust the image contrast.
With contrast adjustment, RGB signals are separated into a luminance signal and color signals without disrupting the color balance, and then the contrast of the luminance signal is adjusted.
Color appears light in areas where the luminance signal level has been increased and, conversely, appears dark in areas where the luminance signal level has been reduced, and leads to an output that is unnatural, and thus the level of the color signal also is increased or decreased in correspondence with the change in the luminance signal level.
The contrast adjustment circuit of a conventional display device is described using FIG. 52. FIG. 52 is a block diagram showing the configuration of the contrast adjustment circuit of a conventional display device. In FIG. 52, a Y matrix 100 converts the R, G, and B signals to a luminance signal Ya. Similarly, a R-Y matrix 101 converts the R, G, and B signals to a R-Y color signal, and a B-Y matrix 102 converts the R, G, and B signals to a B-Y color signal. A gamma correction signal 104 converts the linearity of the luminance signal Ya to a luminance signal Yb. The gamma correction circuit 104 is constituted by a lookup table (hereinafter referred to as “LUT”) such as that shown in FIG. 53, to which table values having gamma correction characteristics are written. Here, the horizontal axis is the input Ya and the vertical axis is the output Yb.
A division circuit 105 divides the luminance signal Yb by the luminance signal Ya to obtain the conversion ratio Yb/Ya. A coefficient unit 106 performs a computation with the conversion ratio Yb/Ya and a coefficient K to obtain a conversion coefficient Kc for amplifying the color signal, where Kc=1+K(Yb/Ya−1). Here, an increase in the color signal can be inhibited by changing the coefficient K. Multipliers 107 and 108 multiply the output of the R-Y matrix 101 and the output of the B-Y matrix 102 by the conversion coefficient Kc, creating a color (R-Y) signal and a color (B-Y) signal that correspond to the adjustment made to the luminance contrast (for example, see Japan Patent Application Publication JP-A-04-152788).
However, contrast adjustment circuits having the above configuration have the problem that for the color signal, the process of obtaining a coefficient for multiplication by the multiplier and then multiplying the color signal by the coefficient that has been obtained is performed after the luminance signal has been divided by the division circuit (the process of dividing the luminance signal includes numerous computations and as such it takes time before the result of the division is output, thus causing a delay), and therefore a discrepancy occurs between the output timing of the luminance signal to be output and the output timing of the color signals to be output, and, additionally, a delay means or the like for synchronizing the timing of the output luminance signal and the output color signals is necessary.
The issue to be solved by the invention is to achieve a visual processing device that can execute precise contrast adjustment on an input image signal and that does not lead to discrepancies in the output timing of the image signal that is output. Another object is to achieve a display device that is provided with this visual processing device, and an integrated circuit that includes this visual processing device.